Figure 4.
B-cell development is arrested at the pre–pro-B-cell stage in Stat5a/bnull/null fetal liver–derived cultures. Fetal livers of 2 embryos of each genotype were pooled (ED 14) and cocultivated on an OP-9 fibroblast feeder layer in the presence of IL-7, Flt-3L, and SCF (10 ng/mL each). Outgrowth of pro-B-cell stages (fractions A-C), immature (fraction E), and mature (fraction F) B cells over a 12-day period is depicted.